Wireless communication devices, such as mobile telephones, include an increasing number of different RF transceivers (radios) to support access to a number of wireless communication services, such as cellular access, local access (e.g., WiFi), ad-hoc connectivity (e.g., Bluetooth), and positioning, such as by the global positioning system (GPS). The cellular radios operate in licensed bands defined by 3GPP. WiFi and Bluetooth both operate in the unlicensed industrial-scientific-medical (ISM) bands at around 2.4 GHz and 5 GHz. Due to the close physical proximity of the transceivers in the device, referred to herein as co-location, and the increasing proximity (in the frequency domain) of the operating frequencies of the transceivers, interaction between the radios becomes more likely, which can cause detrimental performance effects.
With the continuous success of cellular communications, both for voice and data, frequency regulating and specification bodies are constantly seeking make more spectrum available. New cellular radio bands are creeping towards existing bands used for local connectivity. For example Universal Mobile Telecommunications System (UMTS) band 40 (2300-2400 MHz) and UMTS band 7 (2500-2690 MHz) are very close to the 2.4 GHz ISM band (2400-2483.5 MHz) and co-location problems become more likely, potentially leading to mutual interference and/or blocking issues between transceivers operating in different bands. The transmit signals of high-power radio transmitters may impact the sensitivity of the radio receivers. Steep filtering may be required as channels become more closely spaced in frequency (increasing costs, power, and size), but even that may fail when there are no guard bands for the filter to roll off over. For instance, between band 40 and the 2.4 GHz ISM band, no guard band is provided.